What Causes Sap to Drip From a Pine Tree?

Pine trees are part of the genus Pinus and members of the plant family Pineaceae. Resinous evergreens, pine trees retain their needles -- or leaves -- all year long. More than 110 species of pine tree are found worldwide; 35 different species are native to North America. Because of their uniform size, resistance to drought and ease of maintenance, pine trees are integral elements in landscape design. When previously healthy pine trees drip an excessive amount of pitch, the pitch droplets are symptomatic of an insect infestation or disease.

Tiny and difficult to see, pine aphids are small insects with two pipes that extend upward from their abdomen. The insects secret a sticky fluid known as honeydew, which drips from the tree. Gardeners may mistake honeydew for pine pitch, or sap. An infestation of pine aphids consumes the sap of the tree and interrupts food distribution to the branches, stems and needles. A disruption in the pine tree's food supply leads to stunted growth and may kill young trees.

Scotch and white pine trees (Pinus strobus) are especially prone to pine aphid (Cinara strobi) infestations. Pine tree aphids feed in clusters on pine needles, twigs and branches. Aphids lay tiny eggs in rows on the pine needles in late summer. The following spring, several generations of aphids may hatch to feast on the pine tree.

Lady bugs, lacewings, yellow jackets, ground beetles and wasps are natural predators of aphids. You may notice a lot of ants on your pine tree. Ants feed on the honeydew secreted by aphids and tend aphids, protecting them from other natural predators. Chemical control is rarely required to defeat an infestation of pine tree aphids.

Honeydew produced by pine aphids can accumulate on the tree and encourage the growth of sooty mold -- a fungal infection that causes a blackish, crusty mold to develop on the needles and twigs. Pine trees infected with sooty mold produce an abundance of pitch to fend off the fungus. Although sooty mold does not kill the pine tree, the fungus reduces the vigor of the tree, may cause premature needle drop and reduces the aesthetic value of pine trees.

Pine pitch canker (Fusarium circinatum) is a fungal disease that infects all species of pine trees. In California, the Monterey pine (Pinus radiata) is most affected. Pine pitch canker creates lesions that can girdle exposed roots, branches and the trunk of pine trees. Branches droop and wilt as water is disrupted from reaching the tips of the branches. Without water, the needles turn yellow, then reddish brown. The injured pine tree produces large amounts of pitch, or resin, in response to the infection.

Pine pitch canker does not move inside the tree. Each lesion is a separate infection. Pine trees infected with pine pitch canker are susceptible to attack from pine engraver beetles, which cause further damage that may kill the tree.

Bark beetles are tiny black insects about the size of a match head. These members of the insect family Scolytidae attack diseased, drought-stressed and dying trees. The U.S. and Canada are home to more than 600 different species of beetles that can damage or kill healthy trees -- conifers and deciduous trees alike. A healthy pine tree can normally fend off an attack by secreting an excessive amount of sap.

The western pine beetle (Dendroctonus brevicomis LeConte) is especially destructive. Each year of an outbreak kills more than 1 million trees. The western pine beetle is most active at elevations between 2,000 and 6,000 feet. The red-turpentine beetle (Dendroctonus valens LeConte) presents one of the biggest threats to pine trees. The most widely distributed bark beetle in North America, the red-turpentine beetle is found in all parts of the United States except for the Gulf Coast region and the southern Atlantic states. Trees infested with bark beetles often exhibit a heavy covering of pitch tubes.